As a substance having a magnetic resistance effect (characteristics that its resistance value varies under the influence of a magnetic field), III-V group intermetallic compounds have been known. Among them, In-Sb compound (Indium-Antimony compound) is widely known as a substance having high electron mobility which affects sensitivity (i.e., the rate of change in an element resistance value with respect to variation of a magnitude of the magnetic field). Therefore, the In-Sb compound is used as a magnetic resistance element for use in a magnetic sensor.
However, the In-Sb intermetallic compound has in itself an extremely low resistance value. Therefore, when the In-Sb intermetallic compound is used to manufacture a magnetic resistance element, the extremely low resistance value of the In-Sb intermetallic compound makes it difficult to perform impedence matching between the magnetic resistance element and an amplification circuit connected to the magnetic resistance element.
In order to compensate for the foregoing defect of the magnetic resistance element comprising an In-Sb intermetallic compound semiconductor film, measures have been contrived in which, by utilizing the shape effect a vertical-to-transversal side ratio, the magnetic resistance element is made larger so as to increase its resistance value at the sacrifice of its sensitivity, or a large number of the elements, each having a small resistance value, are connected in series so as to increase the resistance value while trying to maintain is sensitivity.
In general, a conventional magnetic resistance element comprising an In-Sb intermetallic compound semiconductor thin film has a configuration as shown in FIG. 4, the configuration being determined on the basis of a principle which will be explained with reference to FIGS. 2 and 3.
FIG. 2 is presented to explain an operational principle of a magnetic resistance element in which a magnetic resistance element 1 comprising an In-Sb intermetallic compound is provided with terminals 2 and 2' at opposing ends thereof. When electricity is applied across these terminals 2 and 2', electrons move along the shortest path between the terminals 2 and 2', as shown in FIG. 2(a), if the magnetic resistance element 1 is not under the influence of a magnetic field B. When the magnetic resistance element 1 is placed in the magnetic field B, electrons move along a curved path as shown in FIG. 2(b). Incidentally, the above-mentioned magnetic resistance effect is subjected to a so-called shape effect. In other words, the magnetic resistance effect depends on the shape of a magnetic resistance element. More particularly, as is apparant from FIGS. 3(a) and 3(b), if the element has a large sides ratio b/a, the rate of change in its resistance value is small with respect to variation in the magnitude of the magnetic field B, that is, the sensitivity of the magnetic resistance element is low although the element resistance value is large.
As described above, the conventional magnetic resistance element comprising an intermetallic compound semiconductor shows unsatisfactory characteristics both for electron mobility and for the element resistance value. To compensate for the low sensitivity, measures have been taken in which a large number of magnetic resistance elements 1 are connected in series with each other, each having a small vertical-to-transversal sides ratio, while on the thin film of the magnetic resistance elements 1, terminals 2 and 2' and short bars 3 are provided by such a method as etching as shown in FIG. 4(a).
However, in the configuration of FIG. 4(a), the magnetic resistance element 1 is long. FIG. 4(b) shows another configuration in which the long magnetic resistance element is folded at several points in order to form the magnetic resistance element in an applicable size and shape.
As mentioned earlier, the In-Sb compound has a low element resistance value, which makes it difficult to perform impedance matching with an amplifier. To obtain the magnetic resistance element of high resistance value, the element is made to be thin (less than 1 .mu.m). In the thin element, however, electron mobility is low, that is sensitivity is low.
As a point of compromise for both electron mobility and element resistance value, a conventional In-Sb intermetallic compound semiconductor thin film is around 1 .mu.m thick and the electron mobility thereof is 1.times.10.sup.4 to 2.times.10.sup.4 cm.sup.2 /V.sec. However, this conventional thin film has an extremely low element resistance value, although the value varies to a certain extent depending on its shape. Accordingly, it was necessary to provide the above-mentioned short bars.
In manufacturing such a conventional In-Sb semiconductor thin film, a vacuum evaporation device containing a vacuum of, for example, 2.times.10.sup.-5 Torr is used. Inside the vacuum evaporation device, a mica substrate is disposed at high temperature on which an In-Sb polycrystal of high purity is deposited to form a thin film. The substrate temperature is kept at a temperature ranging from 380.degree. to 420.degree. C. for the purpose of enhancing the crystal quality and increasing the granule diameter of the In-Sb compound which is deposited. An evaporation source temperature is raised from 900.degree. C. to 1050.degree. C. at a temperature rising speed of about 8.degree. C./min.
A source reports that a film having an electron mobility of 5.times.10.sup.4 to 6.times.10.sup.4 cm.sup.2 /V.sec is obtained at the film thickness of 0.8-1.2 .mu.m by raising a mica substrate temperature from 380.degree. C. to 420.degree. C. at a temperature rising speed of about 2.degree. C./min as the deposition proceeds, so as to maintain the substrate temperature at a low level in the initial period of the deposition so that re-evaporation of Sb deposited on the film is suppressed, thereby maintaining the stoichiometric composition. However, the film is of extremely low resistivity. Another source reports a method in which the mica substrate temperature is kept constant while the evaporation source temperature is increased at a predetermined speed. However, this method also provides an In-Sb semiconductor film of similar characteristics as above.
On the other hand, a conventional III-V group semiconductor thin film such as an In-Sb semiconductor thin film has a low sensitivity due to its low electron mobility. Furthermore, since the film cannot be made thin, its resistance value remains low. In order to enhance its resistance value, it is required to form metal strips called short bars on an element thin film, resulting in a complicated and expensive product.
In view of the foregoing problems, this invention is made. An object of this invention is to provide a thin semiconductor film having a high sensitivity with its resistance value being not lowered, and a method for manufacturing the film by enhancing electron mobility and by preventing reduction in its resistance value.